Diarmaid MacCulloch, a history professor at the University of Oxford, is one of the world's most influential - and at times controversial - church historians. He has written numerous books, including, most recently, a history of Christian silence, and is also an expert on the Reformation. In the late 1980s, Professor MacCulloch was ordained as a deacon in the Church of England, but declined ordination to the priesthood because of the church's attitude to his homosexuality.